The present invention relates to a power supply unit for use in a computer system such as a server computer, a parallel operation control circuit applied to the power supply unit and a parallel operation control method, and more particularly to a power supply unit having a plurality of parallel connected power supply modules and driving the load in accordance with the parallel output from the power supply modules, a parallel operation control circuit applied to the power supply unit and a parallel operation control method.
Some power supply units used in a computer system such as a server computer employ a high reliability power supply system using a redundancy system. As such power supply units employing the high reliability power supply system, those constituted to operate a plurality of power supply modules in parallel are known.
As for the parallel operation, the voltage control system has been well applied. The current balance control system uniformly keeps the output voltages of a plurality of parallel connected power supply modules. In a case where any one of the plural power modules breaks down, if it is removed, the same voltage control can be executed with the remaining power supply modules.
In the power supply unit employing the voltage control system, a circuit for monitoring the output voltages value needs to be provided for each of the power supply modules. Therefore, a transformer for monitoring the voltage is provided at the secondary side of a transformer for voltage transformation, and the output voltage value is detected by the transformer.
In this structure including the transformer for monitoring the voltage, however, the circuit configuration of each power supply module is complicated and enlarged, and as a result, the power supply unit is increased in size and the increase of the manufacturing cost is caused.
In addition, the latest power supply unit is required to support a function of swapping an arbitrary power supply module while keeping the power supply to the computer system such as a server computer, i.e. a function of the in-service swap (also called the hot swap), and for this reason, the structure of the power supply unit is inclined to be more complicated.